This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Among many alternative copyrights managements systems, watermarking techniques hide binary information, called payload, into multimedia content in a robust and imperceptible manner. The embedded information can be used during forensics analysis to identify the source of an illegal copy. However when the watermarked video is camcorded, the watermark payload may be difficult to retrieve because of the impairments due to the capture. In particular, the video may undergo a luminance transform. Unfortunately, this transform will vary along time because of the automatic gain transform of the camcorder. It may also vary spatially because of non homogeneities of the display and the camcorder.
FIG. 1 illustrates prior art methods for detecting a watermark embedded in a video. A current frame 100 in a pirated watermarked video is processed for detecting the value X of the watermark carried by watermarked block 102. The pirated video is compared to the original master video to which the embedding watermark process is applied. A value computed on the watermarked block 103 in the original master video is compared to a value computed on the watermarked block 102 in the pirated video. In a variant, such value is the luminance computed for each sample of the block in the pixel domain representation of a video. Or in another variant, such value is the average luminance computed for the plurality of samples of the block in the pixel domain representation of a video Thus, in the variant of the average luminance, from the comparison between the average luminance of watermarked block 102 in the pirated video and the average luminance of the original block 103 in the master video. The value X of the watermark is determined as being equal to a ‘0’, for instance corresponding to no luminance modification of the original block 103 in the master video or the value X of the watermark is determined as being equal to a ‘1’ corresponding to a luminance modification of the original block 103 in the master video.
The detection method mentioned above will hence be inefficient when the video undergo a luminance transform. And more generally, depending on the value computed on the video, the method is sensitive to video transform. Besides the detection method mentioned above requires temporal registration and spatial registration between the pirated video and the master video in order to align frames 101 from master video and frames 100 of pirated video.
Thus known methods for watermark detection raise the issue of the robustness of the detection in view of luminance modifications or any video transform between master and pirated video.
A method for detecting a watermark embedded in a video resistant to video transform is therefore needed.